T400-4

[Hexhclass]

I repair the PS in this amp,all channels playing good audio but it keeps going in and out of protect.I did not see no dc offset on the channels .When in protect pin 3&4 goes above 4v in the 494

Any suggestions?

 

[Perry Babin]

Photo of board and/or PC #?

 

[Hexhclass]

.

 

[Perry Babin]

52767 driver board?

Thermal protection?

 

[Hexhclass]

Yes 52767 driver board.
I don't no if the behavior is due to thermal.

 

[Perry Babin]

You stated that it was going into protect. Is the protect LED coming on?

 

[Hexhclass]

Yes the protect LED comes on when it starts cycling in and out of protect

 

[Perry Babin]

There is a 'protect' LED and a 'thermal' LED. Which one is coming on?

 

[Hexhclass]

Protect

 

[Perry Babin]

Can you make it go into protect if you move the actuators of the bias pots slightly?

Will it go into protect without driving speakers/loads?

 

[Hexhclass]

It goes into protect with no load.

 

[Perry Babin]

Can you make it go into protect if you move the actuators of the bias pots slightly?

 

[Hexhclass]

I tried all four they didn’t send it in protect.
I forgot to mention when this amp is powered up for the first time it works ok for a while about 10 to 15 minutes before it starts to cycle.

 

[Perry Babin]

Is there any part of the board or any component that you can push on (with a non-conductive probe) to make it go into protect?

Does heating or cooling (inverted can of canned air) cause the amp to go into protect? When using the cooler, I'd suggest having all transistors tightly clamped down and nothing more than a 10 amp fuse inline. If you accidentally spray the bias transistor, it could make the amp draw excessive current.

 

[Hexhclass]

I tried the various methods but could not find nothing .

 

[Hexhclass]

How do I disable the protection? Maybe the problem will show it self after.

 

[Perry Babin]

I've never tried this on this amp, only the older ones, but bridging Q100 collector to emitter should do it. Insert a low rated fuse or limit current to help reduce the risk to the amp.

 

[Hexhclass]

Went back to this amp today, bridging collector to emitter did it stop it from going in protect .

 

[Perry Babin]

...emitter did it stop it from going in protect << Re-read. What did you mean?

 

[Hexhclass]

Sorry
I mean it is still going in protect .